Rabies Confirmed in Two Colorado Horses

Two horses from Colorado's Weld County, located in the northern part of the state, have tested positive for rabies, according to a June 13 statement from the Colorado Department of Agriculture. The horses were on separate premises and their cases are unrelated. So far this year, three Colorado horses have been euthanized after showing severe clinical signs and subsequently testing positive for rabies. The first case was confirmed in Logan County, in the northeastern part of the state, in April.

The CDA is encouraging livestock and pet owners to discuss the need for rabies vaccination with their local veterinarian and to monitor their animals for behavioral changes.

“Animal owners need to primarily look for any dramatic nervous system changes such as muscle tremors, weakness, lameness, stumbling, or paralysis,” said Colorado State Veterinarian Keith Roehr, DVM. "Those are some of the hallmark signs that the animal may be suffering from rabies."

Additional examples of unusual behavior include: wild mammals that show no fear of people and pets; nocturnal animals that are active in daylight; and bats found on the ground, in swimming pools or that have been caught by a pet. Rabid carnivores—such as skunks, foxes, bobcats, coyotes, dogs, and cats—could become aggressive and attempt to bite people, pets and livestock.

Livestock and pet owners are also encouraged to discuss vaccination with their veterinarian for animals that could be exposed to wildlife that carry and could transmit the rabies virus to dogs, cats, horses, small ruminants, llamas, alpacas, and petting zoo animals.

Rabies—a zoonotic disease that can be spread from animals to humans—is caused by a lyssavirus that affects the neurologic system and salivary glands. Horses are exposed most commonly through the bite of another rabid animal.

In horses rabies' clinical signs are variable and can take up to 12 weeks to appear after the initial infection. Although affected horses are sometimes asymptomatic, an infected horse can show behavioral changes such as drowsiness, depression, fear, or aggression. Once clinical signs appear, there are no treatment options.

Rabies can only be diagnosed postmortem by submitting the horse's head to a local public health laboratory to identify the rabies virus using a test called fluorescence antibody. Thus, ruling out all other potential diseases first is very important in these cases to avoid potentially unnecessary euthanasia.

Commercially available rabies vaccines are safe and extremely effective. According to the American Association of Equine Practitioner's vaccination guidelines, adult horses should be vaccinated annually and mares in foal should be vaccinated four to six weeks prepartum or before breeding. Veterinarians should administer an initial series of three vaccines to foals and weanlings younger than 12 months of age; exact timing depends on the mare's vaccination status. Thereafter, horses should be vaccinated annually.

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